This invention relates to a method for soldering an electronic component and an apparatus therefor, and more particularly to an electronic component soldering method and an apparatus therefor wherein preheat and reflow are carried out in turn with time in an oven of a non-closed structure which causes flowing of an ambient atmosphere thereinto, resulting in an electronic component being mounted on a printed board by soldering using paste solder.
A nitrogen gas reflow soldering apparatus was developed for the purpose of elimination of cleaning after soldering of an electronic component using paste solder. The reflow soldering apparatus conventionally known in the art is adapted to carry out soldering in a non-oxidizing atmosphere in an oven charged with nitrogen gas to prevent oxidization of solder alloy and soldered lands, to thereby eliminate use of Freon (trademark), trichloroethylene or the like in the subsequent cleaning operation.
To this end, the conventional reflow soldering apparatus includes an oven body which is constructed into a closed structure so as to keep an oxygen concentration of an atmosphere in the oven body at a level as low as 10 to 100 ppm to minimize consumption of nitrogen. More particularly, the oven body is divided into an inlet nitrogen gas purge chamber section, a preheat and reflow section and an outlet nitrogen gas purge chamber section, wherein the inlet and outlet sections each are provided with a two-stage shutter to isolate a soldering zone in the oven body from an ambient atmosphere. Also, in order to minimize outflow of nitrogen gas from the oven body, a bearing section for a revolving shaft of each of fans arranged in the oven body and each of the shafts are constructed into a closed structure and a conveyor or carrier system is constructed so as to automatically control, in synchronism with operation of the shutters, a speed at which a printed board is fed to the inlet nitrogen gas purge chamber section and discharged from the outlet nitrogen gas purge chamber section.
Although the conventional reflow soldering apparatus constructed as described above ensures satisfactory soldering of an electronic component, it causes an increase in cost of equipment because it is required to construct the oven body into a closed structure. Also, it requires not only a large amount of nitrogen gas but troublesome replacement of a nitrogen gas cylinder when the cylinder is installed as a nitrogen gas source. Further, the reflow soldering apparatus, when a nitrogen gas producing unit is provided in association with the apparatus, causes a further increase in cost of equipment. Nevertheless, when the oven body is constructed into a non-closed structure, the conventional reflow soldering apparatus fails to prevent occurrence of solder holes and formation of an oxide film on solder alloy due to soldering because it does not prevent flow of an ambient atmosphere into the oven body.